pinctrl: pinctrl-single: add header include guard

Add a header include guard just in case.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Link: https://lore.kernel.org/r/20190720115858.7015-1-yamada.masahiro@socionext.comSigned-off-by: Linus Walleij <linus.walleij@linaro.org>

include/linux/platform_data/pinctrl-single.h

 /* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _PINCTRL_SINGLE_H
+#define _PINCTRL_SINGLE_H
+
 /**
  * irq:		optional wake-up interrupt
  * rearm:	optional soc specific rearm function
@@ -11,3 +15,5 @@ struct pcs_pdata {
 	int irq;
 	void (*rearm)(void);
 };
+
+#endif /* _PINCTRL_SINGLE_H */